1. Field of the Invention
This invention relates to an apparatus for calibrating the slit width of the monochromator used for the spectrophotometer.
2. Description of the Prior Art
In a spectrophotometer, the accuracy of the wavelength and the slit width are the most important performance factors affecting the characteristics of the apparatus. Especially in high-class apparatuses, such factors are required to be adjusted to a theoretical limit both structurally and mechanically. Further, such an adjusting mechanism must have an especially rugged construction which can stand vibrations of transportation and changes with time.
In conventional spectrophotometers, a mechanical coupling is used to actuate a wavelength driving means and a slit driving means for the purpose of adjusting the wavelength and slit width.
In other words, the conventional spectrophotometers are such that the wavelength is adjusted by a wavelength adjusting device coupled to a wavelength pickup mechanism or a wavelength counter, and the slit width is adjusted by a stepwise switching system in which the slit width is changed by relocating a slit plate having a plurality of slits or by a continuous variable system in which a pair of slit blades in opposed relation to each other are opened or closed thereby to adjust the slit width continuously. The former system has a high accuracy of slit width but in view of the impossibility to change the slit width continuously, it is used only for comparatively low-class apparatuses. The latter system, on the other hand, which can continuously change the slit width, is used with high-class apparatuses. In the spectrophotometer of the continuously variable type, the slit width is generally indicated by use of a dial or counter mechanically coupled to a slit width changing mechanism. The resulting disadvantage is that if this mechanism is displaced even slightly during transportation or with time, the particular displacement affects the slit width directly, thus reducing the accuracy of the spectrophotometer.